Flat wire stent

ABSTRACT

The present invention concerns an improved stent in which the limbs have been fabricated from a medium having a cross sectional profile in which at least one segment is flat and straight, whereby the stent is provided with improved expansion characteristics.

This application is a continuation-in-part of application Ser. No.08/582,943, filed Jan. 4, 1996, now abandoned.

FIELD OF THE INVENTION

The present invention relates to an improved "stent" for placement incorporeal lumens. More particularly, this invention relates to animproved stent in which the limbs have been fabricated from a mediumhaving a cross sectional profile in which at least one segment isstraight, whereby the stent is provided with improved expansioncharacteristics.

BACKGROUND OF THE INVENTION

The term stent generally refers to a prosthesis, which can be introducedinto a corporeal lumen and expanded to support that lumen or attach aconduit to the inner surface of that lumen.

A number of prior art references are available in the art, each of whichreferences is directed to some specific discrete elements of the systemwhich are described and claimed in the present invention, however, noneof which is directed to the totality of the combination, or its use andfunction in the manner described and claimed herein.

The following prior art references are known to the inventor:

U.S. Pat. No. 4,580,568, which issued to Gianturco on Apr. 8, 1986,discloses an endovascular stent formed of stainless steel wire which isarranged in a closed zig-zag pattern;

U.S. Pat. No. 4,733,665, which issued to Palmaz on Mar. 29, 1988,relates to an expandable intraluminal vascular graft which is expandedwithin a blood vessel using an angioplasty balloon associated with acatheter;

U.S. Pat. No. 4,739,762, which issued to Palmaz on Apr. 26, 1988,teaches an expandable intraluminal graft for use within a bodypassageway or duct which is particularly useful for repairing bloodvessels which have been narrowed or occluded by disease;

U.S. Pat. No. 4,830,003, which issued to Wolff et al on May 16, 1989,discloses a cylindrical shaped stent useful to prevent arterial acuteclosure which is formed of longitudinal wires of biocompatible material,which wires have been welded together in pairs at alternate ends witheach pair or wires bent into a V-section. The wires are formed into acylinder which is welded closed in order to form the stent;

U.S. Pat. No. 5,104,404, which issued to Wolff on Apr. 14, 1992, teachesan intravascular stent which is applied within the peripheral orcoronary arteries of a living animal or a human being in order to returnpatency after a balloon angioplasty. The stent taught in this referenceis an articulated separate stent comprising at least two segments, eachof which segments has a generally tubular shape and a hinge meansextending between and connecting adjoining stent segments;

U.S. Pat. No. 5,019,090, which issued to Pinchuk on May 28, 1991,relates to radially expandable stents which include a plurality ofadjacent generally circumferential sections which are substantiallyaxially positioned with respect to each other;

U.S. Pat. No. 4,886,062, which issued to Wiktor on Dec. 12, 1989,discloses a device which is to be used as a vascular stent comprising acylindrical open-ended wire made of a low memory metal, which ischaracterized by its ability to be expanded radially to a largerdiameter after initial implantation, along with a means for causing saidstent to expand to a larger diameter and a method for transporting,positioning and implantation of such stent;

U.S. Pat. No. 5,370,683, which issued to Fontaine on Dec. 6, 1994, isdirected to a vascular stent for reducing hemodynamic disturbancescaused by angioplasty, said stent being formed from a single filament oflow memory biocompatible material having a series of U-shaped bends. Thefilament is wrapped about a mandril in a circular fashion in order toalign the curved portions of each bend which may then be connected;

U.S. Pat. No. 5,226,913, which issued to Pinchuk on Jul. 13, 1993,teaches a radially expandable stent which includes a plurality ofadjacent generally circumferential sections that are substantiallyaxially positioned with respect to each other, wherein at least one ofthe generally circumferential sections has an expandable segment whichimparts a circumferential and radial expandability to the stent;

U.S. Pat. No. 4,913,141, which issued to Hillstead on Apr. 3, 1990,relates to a stent delivery system for routing the stent to a definedposition within a subject's blood vessel;

U.S. Pat. No. 5,133,732, which issued to Wiktor on Jul. 28, 1992,discloses a stent for implantation into a body vessel comprising acylindrical stent body which has been coiled from a generally continuouswire which has been imparted with a deformable zig-zag structure;

U.S. Pat. No. 5,135,536, which issued to Hillstead on Aug. 4, 1994, isdirected to a stent for reinforcing a vessel wall which is constructedfrom a single elongated wire. The wire has been first bent into a seriesof tight bends and then rolled around a mandril in order to createjunctions of wire which are permanently adhered. The completed stentforms a cylindrical shape which can be expanded from its initialdiameter to a larger implanted diameter by the application of radialoutward force from a balloon catheter;

U.S. Pat. No. 4,655,771, which issued to Wallsten on Apr. 7, 1987,teaches a prosthesis for transluminal implantation comprising a flexibletubular body which has a diameter that is variable by axial movement ofthe ends of the body relative to each other and which is composed ofseveral individual rigid but flexible thread elements each of whichextends in helix configuration with the centerline of the body as acommon axis;

U.S. Pat. No. 5,015,253, which issued to MacGregor on May 14, 1991,discloses a generally tubular stent that includes a non-woven structureformed by two or more generally helically shaped cylinders of stiffstrand material where the strand material forming the non-wovenstructure is preferably secured together at attachment sites which allowthe stent to be flexible and adjustable to meet various needs.

Most manifestations of the available prior art expand by the rotation ofa structural element (limb) from a longitudinal orientation (parallel tothe long axis of the stent) to a more transverse orientation. The limbsthemselves change very little in shape. Stents, in which adjacent limbsare linked to form rings, spirals, or a series of linked rings, expandand contract by deformation of the structural elements in the immediatevicinity of the junction between limbs. In the case of self-expandingstents, the junctions serve as reservoirs of energy, which produce stentexpansion. However, the isolation of mechanical stress to such smallportions of the stent limits the expansion ratio and renders the stentless durable.

An example of this effect is the Gianturco Z-stent ('568). This stent iscomprised of a single loop of wire, in which alternating straightsegments wind back and forth between bends to form a crown. In theGinaturco Z-stent the junctional stresses can be diffused by increasingthe radius of curvature at the bends; the larger the bend the morediffuse the stress. However, large radius bends limit the expansionratio, because the bends take up more space than straight segments.Bending the limbs themselves does little to reduce the stress, becausethese bends are much less amenable to deformation than the bends betweenadjacent limbs. When the stent is compressed, the limbs soon meet alongthe outer curvatures of any bends. Any attempt to further collapse thestent by straightening the limbs is thwarted by the overlapping.

Other stents, which have no rings or spirals of alternating limbs and nofixed junctions between limbs, are free of these problems; however, theyalso lack the expansile energy provided by junctional deformation, andtherefore tend to expand rather weakly. There are currently noself-expanding stents available in the prior art in which the relativepositions of the joined limbs change as a result of deformation that isdistributed over large segments of the limbs.

It is, therefore, an object of the present invention to provide for animproved stent which exhibits superior expansion characteristics overavailable prior art stents.

It is a further object of the present invention to provide for animproved stent in which the limb elements have been fabricated from amedium having a cross sectional profile in which at least one segment isflat and straight, which exhibits superior expansion characteristicsover available prior art stents.

Lastly, it is an object of the present invention to provide for animproved stent which exhibits superior expansion characteristics overavailable prior art stents while at the same time avoiding thecompression and deformation problems associated with other prior artstents.

These and other objects of the invention will become apparent from thefollowing discussion of the invention.

SUMMARY OF THE INVENTION

The present invention provides for an improved stent in which the limbshave been fabricated from a medium having a cross sectional profile inwhich at least one segment is straight, whereby the stent is providedwith improved expansion characteristics.

The construction and obvious advantages of the system provided for bythe present invention will be more clearly understood from the followingdescription of the various specific embodiments when read in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation depicting a single limb elementaccording to the present invention.

FIG. 2 is a schematic representation depicting a single wire comprisingfour limb elements according to the present invention.

FIG. 3 is a schematic representation depicting typical joints betweenadjacent limb elements in a stent which is comprised of a multiplicityof such limb elements.

FIGS. 4A-4D is a schematic representation depicting the progressivecompression of the joint between adjacent limb elements in a stent.

FIG. 5 is a schematic representation of a portion of a stent accordingto the present invention showing the relative geometry of the curvedlimb elements and the joints between adjacent limb elements.

FIG. 6A is a schematic representation of the end of one limb of a stentaccording to the present invention depicting a barb which has beenincorporated therein for anchoring the stent to a lumen wall.

FIG. 6B is a schematic representation of the end of a limb according tothe present invention depicting serrations as an alternative foranchoring the stent to a lumen wall.

FIG. 7 is a schematic representation of the end of a limb according tothe present invention depicting a hole for attachment of a deliverysystem release mechanism, or the like.

FIG. 8 is a schematic representation of an alternative embodiment of thepresent invention depicting a simplified series of limb elements whichhave been attached to adjacent limb elements and the optional additionof a supplemental strut.

FIG. 9 is a schematic representation of an alternative embodiment of thepresent invention depicting a simplified series of limb elements whichhave been attached to adjacent limb elements and the optional additionof two supplemental struts.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an improved stent in which thelimbs have been fabricated from a material having a cross sectionalprofile in which at least one segment is straight, whereby the stent isprovided with improved expansion characteristics as compared withavailable prior art stents.

The problems which have been experienced using prior art stents aresolved in the present invention by creating the stent limbs from amaterial, generally a springy wire material, which has a cross-sectionalprofile in which at least one segment is flat and straight.

Two properties of flat wire are responsible for the principal advantagesof this invention:

1. The flat surfaces of adjacent limb segments of the stent can bepressed together without generating the lateral forces that wouldotherwise cause them to overlap.

2. The mechanical stent limbs can be wide without taking up a largevolume. The width of the limb makes it relatively rigid in the plane ofits largest diameter, which also helps to prevent overlapping.

With reference to the attached figures, it can be seen from FIGS. 1 and5 that a repeating element of each limb 10 of the stent has two curves12 and 14 of equal radius, equal length and opposite direction. Theshort straight segments 16 at the ends of each limb element are parallelto one another. The mid-portion 18 lies between the two curved segmentsof each repeating element of the stent limb. Depending on the overalllength of the stent, the same piece of wire may bend back and forth in asinusoid wave, FIG. 2, to form a series of limb elements 10 down thelength of the stent.

The short straight segments 16 of adjacent limbs are joined, either bywelding, soldering, riveting, or gluing, as depicted in FIGS. 3-9. Amultiplicity of identical limb elements are joined in this way to form acylindrical structure. With reference to FIGS. 3 and 4A-4D, it can beseen that compression of the stent causes adjacent limb elements to bepressed against one another at their junctions 20. Further compressioncauses the curved portions 12 and 14 of adjacent limb elements toflatten progressively. The curves 12 and 14 thereby straighten and thestent assumes a smaller and smaller radius. When the constraining forceis released, the stent expands through re-establishment of the curves 12and 14.

The flat "wire" which is employed in the present invention can be madeof any biocompatible material that is strong, durable and capable ofelastic deformation.

The number of limb elements in each length of wire can be variedaccording to the ratio of length to width required for the specificapplication in which the stent is to be employed. For example, anextended narrowing, as for example in a corporeal lumen such as anartery, a bile duct or an esophagus would require a stent that is muchlonger than it is wide. The individual wires in such a stent wouldtherefore have many limb elements 10, many bends 12 and 14, and manyjoints, since each wire would extend along the entire length of thestent. Alternatively, a stent which is used for anchoring a graft in ashort segment of aorta would have very few limb elements 10, perhapsonly one, in each length of wire.

The radius and length of the curves 12 and 14 can be altered to effectthe orientation of the section of the limb element that lies between thecurves, the mid-section 18. In addition the mid-section 18 may vary inlength as may be required for the particular application. The greaterthe angle described by each curve 12 and 14 in the limb element 10, themore transverse the orientation of the mid-section of the limb, thegreater the shortening produced by stent expansion, the greater theflexibility of the stent, and the greater the resistance to compressionby forces applied in direction of the stent radius. Lengthening themid-section 18 of the limb element magnifies all of these effects.

With reference to FIG. 6A, an alternative embodiment of the end of alimb according to the present invention is shown wherein a barb can beadded by notching 22 the edge of a limb in order to provide a means forattachment of the limb to the inside of a corporeal lumen.

With reference to FIG. 6B, another alternative embodiment of the end ofa limb according to the present invention is depicted, showingserrations 24 as a means for attachment of the limb to the inside of acorporeal lumen.

With reference to FIG. 7, anchor points for delivery system releasemechanisms or for graft attachment are provided for by drilling smallholes 26 in the end of the limbs. The optional features weaken the limbbut have no effect on the structural integrity of the stent if they areplaced in a section of the limb that is not between joints orconnections 20.

The centrifugal expansile force generated by large stents can beincreased by increasing the thickness of the wire. Alternatively, withreference to FIGS. 8 and 9, optional struts 28 can be added to augmentexpansion alone, or augment both the expansile force by increasing therigidity of the composite strut.

It will be further apparent to one skilled in this art that theimprovements provided for in the present invention, while described withrelation to certain specific physical embodiments, also lend themselvesto being applied in other physical arrangements not specificallyprovided for herein, which are nonetheless within the spirit and scopeof the invention taught here.

I claim:
 1. A cylindrical stent which is designed to provide superiorexpansion characteristics within a corporeal lumen comprising aplurality of flat wires extending generally longitudinally along thelength of the stent to form a cylindrical stent having an outer surface,each flat wire having a rectangular cross-section with flat wide sidesand narrow edge sides, each flat wire comprising at least two limbelements; each limb element comprising two curved portion segmentshaving opposite directions of curvature, an intermediate straightmid-portion segment connecting the two curved portion segments and ashort-straight segment connected to each curved portion segment at eachend of each limb element; each short-straight segment of each limbelement being joined to the adjacent short-straight segment of a limbelement of an adjacent flat wire to form the cylindrical stent surface;the flat wide sides of each flat wire being radially perpendicular tothe cylindrical stent surface.
 2. The improved stent according to claim1 wherein each wire is equal in length.
 3. The improved stent accordingto claim 1 wherein each limb element is equal in length andconfiguration.
 4. The stent according to claim 1 wherein each wire has aplurality of identical limb elements in series.
 5. The stent accordingto claim 1 wherein each flat wire is bent back and forth in a sinusoidalwave pattern to form a series of limb elements along the length of thewire.
 6. The stent according to claim 1 wherein said short-straightsegment of said limb element at the end of at least one of said flatwire is elongated and an edge of said elongated short-straight segmentis serrated as an anchor point for attachment of the stent to the insideof a corporeal lumen.
 7. The stent according to claim 1 wherein saidshort-straight segment of said limb element at the end of at least oneof said flat wire is elongated and barbed as an anchor point forattachment of the stent to the inside of a corporeal lumen.
 8. The stentaccording to claim 1 wherein said short-straight segment of said limbelement at the end of at least one of said flat wire is elongated andhas a hole as an anchor point for a delivery system release mechanism ora graft attachment.
 9. The stent according to claim 1 wherein saidshort-straight segment of said limb element at the end of at least oneof said flat wire is elongated and the edges of said elongatedshort-straight segment and said adjacent short-straight segment to whichit is joined are serrated as an anchor point for attachment of the stentto the inside of a corporeal lumen.
 10. The stent according to claim 1wherein said stent has at least one strut to augment stent expansion andto resist stent compression, said strut having a shorter length thansaid limb element and having two curved portions having oppositedirections of curvature, an intermediate straight, flat mid-portionconnecting the two curved portions, and a short-straight segmentconnected to each curved portion at each end of said strut, one of saidshort-straight segments of said strut being joined to saidshort-straight segment of said limb element and lying in saidcylindrical stent outer surface, said strut positioned between adjacentlimb elements of adjacent wires.
 11. A stent according to claim 1wherein said stent has at least one strut having a length substantiallyidentical to one of said limb elements to augment stent expansion and toresist stent compression, said strut having two curved portions havingopposite directions of curvature, an intermediate straight mid-portionconnecting said two curved portions, and a short-straight segmentconnected to said curved portion at each end of said strut, said strutbeing positioned parallel to said limb element of said short-straightsegment the and lying in said cylindrical stent outer surface, saidshort-straight segment of said strut being attached to saidshort-straight segment of said limb element.
 12. A cylindrical stentwhich is designed to provide superior expansion characteristicscomprising limbs which have been fabricated from a plurality of flatwires having a flat rectangular cross-sectional profile having wide flatsides and narrow edge sides, said limbs being formed out of repeatingelements, each limb being comprised of two curved portions havingopposite directions of curvature, an intermediate straight mid-portionsegment connecting said two curved portions and a short-straight segmentat each end of the curved portions, adjacent wires being joined on theirwide flat sides by having the short-straight segment of each limbelement joined to the short-straight segment of a limb element of anadjacent flat wire to form said cylindrical stent having an outersurface, said stent having been provided with at least one strut inorder to augment expansion wherein said strut has been effectivelyattached at a point of attachment between said adjacent limb elements,each limb element and each strut lying in said cylindrical, stent outersurface said wide, flat sides of each wire being radially perpendicularto said cylindrical stent outer surface.
 13. A cylindrical stent whichis designed to provide superior expansion characteristics comprisinglimbs which have been fabricated from a plurality of flat wires having aflat rectangular cross-sectional profile having wide, flat sides andnarrow edge sides, said limbs being formed out of repeating elements,each limb being comprised of two curved portions having oppositedirections of curvature, an intermediate straight mid-portion segmentconnecting said two curved portions and a short-straight segment at eachend of said curved portions, adjacent wires being joined on their wideflat sides by having the short-straight segment of each limb elementjoined to the short-straight segment of a limb element of an adjacentflat wire to form said cylindrical stent having an outer surface, saidstent having been provided with a multiplicity of struts to supplementeach of the limb elements which have been effectively attached at bothends to a point of attachment between adjacent limb elements, each limbelement and each strut lying in said cylindrical stent outer surface,said wide, flat sides of each wire being radially perpendicular to saidcylindrical stent outer surface.